Why is Impeachment Article 8: Invading Iraq against international law not a good reason?

Some mentioned this and want to know why. It is clear we are signatory to many international treaties that make it illegal to attack another nation that is not a threat. Clearly, since Iraq had no weapons of m destruction or no ties to terrorists, Iraq was not a threat. Indeed, under the other George Bush , we more sold chemical weapons to Saddam Hussein after he used them in the Iraq-Iran war. Hussein also had no air force, and was really under our control.